Organic polysulfides and particularly dialkyl polysulfides such as tetra- and penta-sulfides have been found useful for many purposes such as additives or elastomers, antioxidants for lubricating oils, intermediates for the production of organic chemicals, insecticides, germicides and as an additive to diesel fuels to improve the cetane number and ignition qualities of these fuels. These compounds have also found useful in the compounding of extreme pressure lubricants and in the acceleration of rubber treating processes.
Such polysulfide compounds can be prepared by reacting mercaptans with elemental sulfur in the presence of a basic catalyst. For example, Biensan et al (U.S. Pat. No. 3,308,166) discloses that polysulfides can be prepared from a mercaptan and sulfur catalyst by an amine using an alcohol promoter.
A conventional process for producing a polysulfide compound such as di-t-dodecyl polysulfide is to react a mercaptan such as t-dodecylmercaptan with elemental sulfur in the presence of a catalyst. However, the polysulfide thus prepared is associated with some unreacted mercaptans and residual H.sub.2 S contributing to unpleasant odor. Additionally, possibly because of the unreacted mercaptans, the product always becomes very unstable, i.e., the product turns cloudy, probably due to degradation of the polysulfide causing precipitation of sulfur. The instability along with the unpleasant odor greatly reduce the desirability and utility of the polysulfide product.
There is therefore a need to remove the odor associated with the product and to stabilize the product. For example, European Patent Application 76 376 (Apr. 4, 1993) discloses that a newly synthesized crude polysulfide can be deodorized by treating the crude polysulfide with a metal salt of an inorganic or organic acid at an elevated temperature. However, the process disclosed therein requires a lengthy treatment in order to obtain a satisfactory result. The reference process also discloses that powdered an hydrous salt is preferred. Powdered anhydrous salt generally is more expensive than a hydrate salt and requires additional processing cost for producing the powdered form. It would therefore be a significant contribution to the art to develop an improved process for the stabilization and deodorization of a crude polysulfide product so that the product is made more useful for industrial uses.